Irregular Chain Research Articles

Effect of short-chain branching on interfacial polymer structure and dynamics under shear flow.

We present a detailed analysis on the effect of short-chain branches on the structure and dynamics of interfacial chains using atomistic nonequilibrium molecular dynamics simulations of confined polyethylene melts in a wide range of shear rates. The intrinsically fast random motions of the short branches constantly disturb the overall chain conformation, leading to a more compact and less deformed chain structure of the short-chain branched (SCB) polymer against the imposed flow field in comparison with the corresponding linear polymer. Moreover, such highly mobile short branches along the backbone of the SCB polymer lead to relatively weaker out-of-plane wagging dynamics of interfacial chains, with highly curvy backbone structures in the intermediate flow regime. In conjunction with the contribution of short branches (as opposed to that of the backbone) to the total interfacial friction between the chains and the wall, the SCB polymer shows a nearly constant behavior in the degree of slip (ds) with respect to shear rate in the weak-to-intermediate flow regimes. On the contrary, in the strong flow regime where irregular chain rotation and tumbling dynamics occur via intensive dynamical collisions between interfacial chains and the wall, an enhancement effect on the chain detachment from the wall, caused by short branches, leads to a steeper increase in ds for the SCB polymer than for the linear polymer. Remarkably, the SCB chains at the interface exhibit two distinct types of rolling mechanisms along the backbone, with a half-dumbbell mesoscopic structure at strong flow fields, in addition to the typical hairpin-like tumbling behavior displayed by the linear chains.

Syntheses, structural diversity and photocatalytic properties of two rare Ni(II) coordination polymers assembled by “V”-shaped dicarboxylates and bis(imidazolyl) ligands

Two novel coordination polymers, namely {[Ni2(dpb)(Hdpb)2(4,4′-bbibp)2(H2O)]·H2O}∞ (1) and [Ni(dpb)(bimb)(H2O)]∞ (2) (H2dpb=3,5-di(4′-carboxyl-phenyl)benzene acid, 4,4′-bbibp=4.4′-bis(benzoimidazo-1-ly)biphenyl, bimb=1.4-bis(imidazol-1-ylmethyl)benzene) have been synthesized under hydrothermal conditions and characterized by elemental analysis, IR spectra, powder X-ray diffraction (PXRD), thermogravimetric (TG) analysis and single-crystal X-ray diffraction. Complex 1 shows a rare 1D meso-helical ladder chain, and the adjacent 1D irregular ladder chain forms a 3D supramolecular framework through the OH⋯O and CH⋯π interactions. Complex 2 exhibits an unprecedented 2-nodal (2,4)-connected 2D layer structure with the Schläfli point symbol (84·122)(82), which are further assembled into a 3D supramolecular structure also by OH⋯O interactions. Furthermore, the photocatalytic properties of complexes 1 and 2 have been investigated. Interestingly, complex 2 not only shows an remarkable photocatalytic activity on RhB/MB degradation, but also has a better adsorption activity based on the bigger channel under magnetically stirred in the dark for 30min.

Microstructural PALS study of regulated dimethacrylates: Thiol‐ versus β‐allyl sulfone‐based networks

ABSTRACTRadical photocuring of multifunctional (meth)acrylates is lacking control over the irregular chain growth process yielding highly crosslinked, inhomogeneous networks. Chain transfer agents (CTAs, e.g., thiols or β‐allyl sulfones) have been widely used to modify this curing process, thus reducing shrinkage stress and increasing the toughness of the formed photopolymers. Resulting photopolymer networks exhibit higher bulk density, lower crosslinking density, and narrow glass transitions. Consequently, a more homogeneous network structure was postulated for those networks. Whereas macroscopic properties of the modified final materials have already been studied, herein the microstructural arrangement of such modified networks has also been evaluated with the help of positron annihilation lifetime spectroscopy (PALS). A more homogenous network structure with a decreased average free‐volume void size was confirmed for CTA‐based dimethacrylate networks. A sharper distribution of the ortho‐positronium (o‐Ps) lifetime, mainly for the β‐allyl sulfone‐based photopolymers, hints toward a more regulated network structure. Moreover, the combination of PALS, DMTA, density and swelling experiments elucidates relations between void formation, crosslinking density and macroscopic characteristics such as shrinkage stress and mechanical properties. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 2476–2484

Synthesis, helicity, thermal stability, and low infrared emissivity of optically active polyacetylenes carrying tyrosine pendants

Optically active polyacetylenes (LPA and DPA) and racemic polyacetylenes (RPA) were prepared by the polymerization of N-propioloyl-tyrosine methyl esters that derived from chiral and racemic tyrosine. All the polymers were characterized by Fourier transform infrared spectroscopy, 1H NMR, 13C NMR, gel permeation chromatography, thermogravimetric analysis, UV–vis spectroscopy, and circular dichroism spectroscopy; furthermore, the infrared emissivity values were also investigated. Both LPA and DPA possessed the helical conformations and a higher degree of intra- and interchain hydrogen bonds compared with RPA, which presented irregular polymer chain. The thermal stability of LPA and DPA was higher than that of RPA due to the helical conformations, which could be easy to form a high degree of intra- and interchain hydrogen bonds in the structure. Therefore, LPA and DPA exhibited lower infrared emissivity values (8–14 μm) than that of RPA, which resulted from the helical conformations and a higher degree of in...

Synthesis, helicity, thermal stability, and low infrared emissivity of optically active polyacetylenes carrying tyrosine pendants

Optically active polyacetylenes (LPA and DPA) and racemic polyacetylenes (RPA) were prepared by the polymerization of N-propioloyl-tyrosine methyl esters that derived from chiral and racemic tyrosine. All the polymers were characterized by Fourier transform infrared spectroscopy, 1H NMR, 13C NMR, gel permeation chromatography, thermogravimetric analysis, UV–vis spectroscopy, and circular dichroism spectroscopy; furthermore, the infrared emissivity values were also investigated. Both LPA and DPA possessed the helical conformations and a higher degree of intra- and interchain hydrogen bonds compared with RPA, which presented irregular polymer chain. The thermal stability of LPA and DPA was higher than that of RPA due to the helical conformations, which could be easy to form a high degree of intra- and interchain hydrogen bonds in the structure. Therefore, LPA and DPA exhibited lower infrared emissivity values (8–14 μm) than that of RPA, which resulted from the helical conformations and a higher degree of intra- and interchain hydrogen bonds.

The Catalytic Subunit of the SWR1 Remodeler Is a Histone Chaperone for the H2A.Z-H2B Dimer

Histone variant H2A.Z-containing nucleosomes exist at most eukaryotic promoters and play important roles in gene transcription and genome stability. The multisubunit nucleosome-remodeling enzyme complex SWR1, conserved from yeast to mammals, catalyzes the ATP-dependent replacement of histone H2A in canonical nucleosomes with H2A.Z. How SWR1 catalyzes the replacement reaction is largely unknown. Here, we determined the crystal structure of the N-terminal region (599-627) of the catalytic subunit Swr1, termed Swr1-Z domain, in complex with the H2A.Z-H2B dimer at 1.78 Å resolution. The Swr1-Z domain forms a 310 helix and an irregular chain. A conserved LxxLF motif in the Swr1-Z 310 helix specifically recognizes the αC helix of H2A.Z. Our results show that the Swr1-Z domain can deliver the H2A.Z-H2B dimer to the DNA-(H3-H4)2 tetrasome to form the nucleosome by a histone chaperone mechanism.

The Catalytic Subunit of the SWR1 Remodeler has a Histone Chaperone Role for the H2A.Z-H2B Dimer

Histone variant H2A.Z-containing nucleosomes exist at most eukaryotic promoters and play important roles in gene transcription and genome stability. The multi-subunit nucleosome-remodeling enzyme complex SWR1, conserved from yeast to mammals, catalyzes the ATP-dependent replacement of histone H2A in canonical nucleosomes with H2A.Z. The over-incorporation of H2A.Z in chromatin, however, is associated with breast cancer, and therefore H2A.Z and p400/SRCAP are targets for cancer therapy. How SWR1 catalyzes the replacement reaction is largely unknown. Here we determined the crystal structure of the region (599-627) of the catalytic subunit Swr1, termed Swr1-Z domain, N-terminal to the ATPase domain, in complex with the H2A.Z-H2B dimer at 1.78 A resolution. The Swr1-Z domain forms a 3(10) helix and an irregular chain, separated by an 8-residue disordered loop. Swr1-Z forms hydrophobic interactions with the a3 and aC helices of H2A.Z, and also with the a1 and a2 helices of H2B. Importantly, a conserved LxxLF motif in the Swr1-Z specifically recognizes the αC helix of H2A.Z, which leads to an extension of two helical turns of the aC helix in H2A.Z. Additionally, the Asp-rich region in Swr1-Z forms electrostatic interactions with Arg85 in the L2 loop, and with Arg89 in the a3 helix of H2A.Z, and with Lys60 in the a2 helix of H2B, which makes the complex more stable. Furthermore, in vitro studies show that Swr1-Z domain can deliver the H2A.Z-H2B dimer to the DNA-(H3-H4)2 tetrasome to form the nucleosome by a histone chaperone mechanism, and in vivo studies indicate that Swr1-Z has an important functional role. Our results provide the first structural insights into how Swr1 recognizes H2AZ-H2B, and help identify similar binding regions between human H2AZ-H2B and p400/SRCAP, paving the road for structure-based cancer drug design.

Detecting Powered-Two-Wheeler incidents from high resolution naturalistic data

During risky conditions, Powered-Two-Wheeler (PTW) drivers often alter their behavior from a regular driving pattern to an irregular chain of driving actions by braking, changing the throttle pressure, maneuvering and so on, or combinations of the above. However, both the actual and perceived thresholds of regular and irregular driving behavior differ among PTW drivers. A simple and flexible methodology is proposed in order to define PTW driving profiles by distinguishing between regular and irregular PTW driving behaviors using high resolution naturalistic data. “Irregularities” in driving behavior are consistently expressed as outlying values in the dataset of driving parameters. The detected irregularities are those that diverge from the centroid of the jointly considered driving parameters. These irregularities may be considered to define critical driving situations (incidents) that are further associated to typical driving events. Results indicate that the joint consideration of variables which are directly connected to the mechanical characteristics of PTW, such as front and rear brake activation, wheel speed, throttle and steering, are adequate to distinguish the regular from irregular PTW driving behavior.

More Phenolic Derivatives with an Irregular Sesquiterpenyl Side Chain from Macaranga pruinosa

More Phenolic Derivatives with an Irregular Sesquiterpenyl Side Chain from Macaranga pruinosa

Anion Photoelectron Spectroscopy and Density Functional Study of Small Aluminum−Vanadium Oxide Clusters

Small aluminum-vanadium oxide clusters, AlVO(y)(-) (y = 1-3) and Al(x)VO(2)(-) (x = 2, 3), were investigated with anion photoelectron spectroscopy and density functional calculations. The adiabatic detachment energies of AlVO(y)(-) were estimated to be 1.06 ± 0.05, 1.50 ± 0.08, and 2.83 ± 0.08 eV for y = 1, 2, and 3. Those of Al(2)VO(2)(-) and Al(3)VO(2)(-) were estimated to be 1.22 ± 0.08 and 1.25 ± 0.08 eV. Comparison of theoretical calculations with experimental measurement suggests that the most probable structure of AlVO(-) cluster is quasilinear with O atom in the middle. AlVO(2)(-) has an irregular chain structure of Al-O-V-O and a C(2v) cyclic structure very close in energy. The structure of AlVO(3)(-) cluster is evolved from the C(2v) cyclic AlVO(2)(-) structure by adding the third O atom to the V atom. Al(2)VO(2)(-) has a pair of nearly degenerate Al-O-V-O-Al chain structures that can be considered as cis and trans forms. Al(3)VO(2)(-) probably has two low-lying isomers each containing a four-membered ring. The structures of the corresponding neutral clusters are discussed.

5,10,15,20-Tetra-(N-methyl-3-pyridyl)porphyrin destabilizes the antiparallel telomeric quadruplex d(TTAGGG)4

We studied the parameters of binding of 5,10,15,20-tetra-(N-methyl-3-pyridyl)porphyrin (TMPyP3) to the anti-parallel human telomeric G-quadruplex d(TTAGGG)4, the oligonucleotide dTTAGGGTTAGAG(TTAGGG)2 that does not form a quadruplex structure, as well as to the double stranded d(AC)8 x d(GT) and single stranded d(AC)8 and d(GT)8 DNAs. The analysis of absorption revealed that the binding constants and the number of DNA binding sites for TMPyP3 were d(AC)8 < d(GT)8 < d(AC)8 x d(GT)8 = d(TTAGGG)4 < dTTAGGGTTAGAG(TTAGGG)2. We demonstrated for the first time that the binding constant of TMPyP3 with the non-quadruplex chain dTTAGGGTTAGAG(TTAGGG)2 (1.3 x 10(7) M(-1)) is approximately 3 times bigger than the binding constant with the quadruplex d(TTAGGG)4 (4.6 x 10(6) M(-1)). Binding of two TMPyP3 molecules to d(TTAGGG)4 led to a decrease of thermostability of the G-quadruplex (deltaT(m) = -8 degrees C). Circular dichroism spectra of TMPyP3:d(TTAGGG)4 complexes revealed a shift of DNA structure from the G-quadruplex to an irregular chain. We hypothesize that partial destabilization of the telomeric G-quadruplex by TMPyP3 might be a reason for relatively low potency of this ligand as a telomerase inhibitor, as well as its marginal cytotoxicity for cultured tumor cells.

Static properties of polymer melts in two dimensions

Self-avoiding polymers in strictly two-dimensional (d=2) melts are investigated by means of molecular dynamics simulation of a standard bead-spring model with chain lengths ranging up to N=2048. The chains adopt compact configurations of typical size R(N)∼Nν with ν=1/d. The precise measurement of various distributions of internal chain distances allows a direct test of the contact exponents Θ0=3/8, Θ1=1/2, and Θ2=3/4 predicted by Duplantier. Due to the segregation of the chains the ratio of end-to-end distance Re(N) and gyration radius Rg(N) becomes Re2(N)/Rg2(N)≈5.3&amp;lt;6 for N⪢100 and the chains are more spherical than Gaussian phantom chains. The second Legendre polynomial P2(s) of the bond vectors decays as P2(s)∼1/s1+νΘ2, thus measuring the return probability of the chain after s steps. The irregular chain contours are shown to be characterized by a perimeter length L(N)∼R(N)dp of fractal line dimension dp=d−Θ2=5/4. In agreement with the generalized Porod scattering of compact objects with fractal contour, the Kratky representation of the intramolecular structure factor F(q) reveals a strong nonmonotonous behavior with qdF(q)∼1/(qR(N))Θ2 in the intermediate regime of the wave vector q. This may allow to confirm the predicted contour fractality in a real experiment.

Phenolic Derivatives with an Irregular Sesquiterpenyl Side Chain from Macaranga pruinosa

A stilbene and two flavonoid derivatives, macapruinosins A-C (1-3), together with two known flavonoids, papyriflavonol A and nymphaeol C, have been isolated from the acetone extract of the leaves of Macaranga pruinosa. The structures of these compounds were identified based on spectral data analysis. Compounds 1 and 2 are the first examples of natural compounds containing an irregular sesquiterpenyl side chain with a cyclobutane skeleton.

Nonisothermal Crystallization Behaviors of Flame-Retardant Copolyester/Montmorillonite Nanocomposites

In order to obtain poly(ethylene terephthalate) (PET) engineering plastics with good flame retardancy, heat resistance, and mechanical properties, a novel phosphorus-containing copolyester (PET-co-DDP)/organo-montmorillonite (OMMT 1%) nanocomposite (PET-co-DDP/OMMT) was prepared by in situ intercalating polymerization. Nonisothermal crystallization kinetics and nanoscale morphology of this composite have been investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and differential scanning calorimetry (DSC). Based on the results of the nonisothermal crystallization kinetics, the flame-retardant copolyester PET-co-DDP has a lower crystallization rate than pure PET, while PET-co-DDP/OMMT nanocomposite has a higher crystallization rate than pure PET. Based on the Augis and Bennett method, the activation energies for nonisothermal crystallization of pure PET, PET-co-DDP, and PET-co-DDP/OMMT nanocomposite were evaluated as 101, 138, and 76 kJ mol−1, respectively. All the evidence shows that PET-co-DDP strongly influences the crystallization behavior because of its irregular chain structure, while the addition of nanoscale OMMT to this copolymer can significantly enhance the crystallization rate owing to its remarkable nucleating effect. An understanding of the above crystalline behaviors will be beneficial in preparing PET engineering plastics with good overall comprehensive performance.

NMR structure of chaperone Chz1 complexed with histones H2A.Z-H2B.

The NMR structure of budding yeast chaperone Chz1 complexed with histones H2A.Z-H2B has been determined. Chz1 forms a long irregular chain capped by two short α-helices, and uses both positively and negatively charged residues to stabilize the histone dimer. A molecular model that docks Chz1 onto the nucleosome has implications for its potential functions.

Perturbing effects of bulky comonomers on the chain conformation of poly(vinylidene fluoride)

The comonomer effect on the structures of poly(vinylidene fluoride–hexafluoropropylene) P(VDF–HFP) copolymers was analyzed by Raman spectroscopy. The HFP content of these copolymers varies from 5% to 15%. Because of steric interactions involving the bulky HFP comonomers, the predominant chain conformation has extensively more gauche conformers in comparison to the neat PVDF. Based on both experimental and simulation studies, specific spectroscopic features in the 400–900cm−1 region have been identified that are characteristic of irregular chain conformations elucidating the perturbing effect of HFP on the equilibrium chain statistics of PVDF in the amorphous phase. In addition, these spectroscopic features were revealed to be extremely sensitive to the relative placements of the CF3 units with respect to other fluorine atoms along the chain.

Specifics of the composition of monocyclic aromatic hydrocarbons in asphaltite from the Ivanovskoe deposit

The molecular composition of alkyl substituted monocyclic aromatic hydrocarbons from asphaltite of the Ivanovskoe deposit was analyzed by means of the gas chromatography-mass spectrometry technique. Unlike most crude oils and natural bitumens, asphaltite is characterized by an unusual composition of practically all isobaric-homologous series of this class of hydrocarbons. The specific features of the composition of these series is a strong prevalence of C12-C23 1-alkyl-2,3,6-trimethylbenzenes with an irregular isoprenoid chain. These compounds are derivatives of isorenieratene, a carotenoid that occurs in anoxic photosynthetic green sulfur bacteria of the Chlorobiaceae family (Chlorobium genus). The ortho-isomers evidently prevail among C13-C25 alkyltoluenes, thus indicating a low level of catagenetic transformation of the asphaltite. n-Alkylbenzenes are practically absent from the monoalkylbenzene series; these are represented by the complete set of C17-C19 phenylalkanes. Such compounds were detected for the first time in natural bitumens.

ATRP of Allyl Methacrylate with Alkyl Methacrylates – Crosslinking of Poly(methacrylate)s with Allyl Ester Side Groups

AbstractSummary: Random copolymers of methyl methacrylate (MMA), butyl methacrylate (BMA) and allyl methacrylate (AMA) were prepared via atom transfer radical polymerization (ATRP). AMA is a bifunctional monomer with two double bonds of different reactivity: a highly reactive methacrylate double bond and an allyl ester double bond of lower reactivity. In order to obtain linear polymers with pendant allyl ester groups, the copolymerization conditions have to be optimized with respect to the concentration of AMA, the catalyst system applied – especially the ligand – and the temperature. By means of kinetic studies the reaction parameters for a controlled polymerization were determined. The results obtained show that the higher the temperature and the amount of AMA is the higher is the probability of irregular chain growth and side reactions induced by the pendant allyl ester groups such as hydrogen abstraction from the allyl position or radical addition to the allyl ester double bond. The random copolymers were photochemically crosslinked by using 2,2‐dimethoxy‐2‐phenylacetophenone as photoinitiator. The thermal properties of linear and crosslinked polymers were determined. The glass transition temperatures of both show no significant difference at low AMA content and thus low crosslinking densities.GPC eluograms of MMA/BMA (70:30) copolymers with 5 mol‐% AMA at different conversions.magnified imageGPC eluograms of MMA/BMA (70:30) copolymers with 5 mol‐% AMA at different conversions.

Facilitating the arrival of illegal immigrants in the Netherlands: Irregular chain migration versus smuggling chains

What role do human smuggling organizations play in facilitating the arrival of (illegal) immigrants in the Netherlands and their further incorporation into Dutch society? Based on empirical research among 325 illegal immigrants living in the Netherlands, the question of how illegal immigrants succeeded in scaling the walls of the European Union and settling in the Netherlands is addressed. Answering this question clarifies not only the role of human smuggling organizations but also that of loyal relatives living in the Netherlands for the continuation of the irregular migration process.

Strength and deformation of rigid polymers: structure and topology in amorphous polymers

Glassy polymer is formed because the irregular chain architecture prevents crystallisation. Computer simulations allow Voronoi tessellation of atomic groups (for example monomers) to be carried out and measured along the molecular chain, which reveals significant density fluctuations. A Voronoi polyhedron is constructed for each particle according to a unique mathematical procedure [J Reiner Angew Math 134 (1908) 198]. When measured in terms of Voronoi polyhedra, amorphous structures show wide variations in packing density on the atomic/monomer scale, with a characteristic skewed distribution. The Voronoi method can be applied to all polymers; however, in this paper only uncrosslinked amorphous polymers are considered. Constriction points around a chain segment are defined as a locally specific configuration and arrangement of adjacent chains such that the local density within a sphere of radius approximately equal to two monomer diameters comes close to or below the hypothetical crystalline density. The topological theory of molecular structure developed by Bader defines the concepts of atoms and bonds in terms of the topological properties of the observable charge distribution [Rep Prog Phys 44 (1981) 893]. In polymers the high density regions become an even stronger topological feature, and are referred to as the constriction points.